ikon31
Retro Apprentice
Posts: 51
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Post by ikon31 on Apr 11, 2011 17:23:59 GMT
After getting the bike sorted after the puncture, disaster!!
was riding out coz of the loverly weather and about 2 mile from home i got onto a national speed limit, just hit 60 and bike started making bad sounds, lots of popping and misfire. Great loss of power, so much so i coasted down to 20mph and in the end stopped. Bike started again and i limped home (possible on one cylinder) at 15mph.
So details as..... cb250n, fitted with cone filters, and a 2into1 motad. Its not been jetted (to my knowledge) i was going to get round to it but bike ran perfect... so not sure if this may have caused it.
Ive fitted a new plug, and i got a right belt of the ht lead messing with it while it was running and it came off in my hand!! (dont try this at home..ouch) so again assume its got power and is sparking... is it possible its not sparking but power in the lead... i could swap the leads? or would that not work due to the firing sequence (as you can tell i'm new to engines)
Its misfiring, think its running on only the right cylinder. The left exhaust header doesn't get hot like the right side does. The carbs have single fuel feed and im assuming fuel is getting through, unless one jet is blocked??
This evening i ran it for a few seconds and then looked at the plug, smelt like fuel but again couldnt be certain, however when i had the plug out i noticed smoke/vapour coming out the hole....... my theory.....
the exhaust has been poorly fitted and leaking from the seal (i believe this to be true) because of this something has happened to the exhaust valve on the left cylinder, causing was appears to be a misfire?
I dont know, any ideas... i suppose whipping it out and taking it apart would be the best bet.
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Post by garryl on Apr 11, 2011 19:11:08 GMT
Start with the basic's....
After starting (or trying to start) remove the plug, is wet/oily? indicating no (or poor) sparking, or dry with no smell of fuel indicating lack of petrol?.
If the former then while the plug is removed, re-attach the plug lead and hold the plug onto the cylinder head and at the same time turn the engine over, you 'should' see a strong spark at the plug tip. If not then you need to check/replace the plug and check/replace the leads, points/condensor (if it has them)
If you have a dry plug then you need to start looking at the carbs, if all the above is Ok then it might be worth a compression test to see if you have a dodgy valve.
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Post by tee-one on Apr 12, 2011 9:08:06 GMT
Id try for air leaks on that cylinder/inlet... And get a plug out, Get a torch and look down at the piston. See if its been holed.
I was having similar trouble with the puch the other week. Turned out to be a airleak where the carb meets the inlet.
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ikon31
Retro Apprentice
Posts: 51
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Post by ikon31 on Apr 13, 2011 13:12:25 GMT
airleak where the carb meets the inlet. thats an intresting one, as there was fuel on the outside of the carb by the time i had got it home... i've got spark, gonna check its getting fuel later, and pick up a compression tester on my way home from work.
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Post by deegee99 on Apr 16, 2011 12:23:47 GMT
CB250N, I think I'm right in saying that they use CV (constant velocity) carbs, common problem on these is the diaphragm splits and you lose a cylinder, slide does not do what you want it to do, spitting, misfire, no go on that cylinder depending on the state of the diaphragm. Easy check just undo the screws holding the top on and check the rubber for splittage. On an old Honda these can go just like that, especially if you just decided to give it a handful.
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ikon31
Retro Apprentice
Posts: 51
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Post by ikon31 on Apr 18, 2011 18:34:26 GMT
i've got no compression on that cylinder, looks to me like the timing chain has slipped, as it looks a little slack to me, and the motion of the valves on that cylinder doesn't look as smooth as that on right cylinder.
Gonna see if i can pick up a motor cheap enough, if not i'll have to drop it and rebuild it
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Post by garryl on Apr 18, 2011 19:15:27 GMT
i've got no compression on that cylinder, looks to me like the timing chain has slipped, as it looks a little slack to me, and the motion of the valves on that cylinder doesn't look as smooth as that on right cylinder. Gonna see if i can pick up a motor cheap enough, if not i'll have to drop it and rebuild it If the cam chain has slipped a tooth this shouldn't 'in itself' cause no compression (unless the piston has hit and bent a valve). I'd be tempted to whip the head off and check the valves/ piston before writing off the engine.
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ikon31
Retro Apprentice
Posts: 51
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Post by ikon31 on Apr 18, 2011 21:46:08 GMT
well i've found a good motor for £60, i'm gonna buy that, chuck it in so i can use the bike in the mean time, so i can take the old to bits and investigate properly.
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ikon31
Retro Apprentice
Posts: 51
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Post by ikon31 on Apr 27, 2011 19:36:04 GMT
ooops, well only got myself to blame, turns out the new motor doesn't work right either, it sounded a bit rough, and i thought oh it will just be the carbs running through, maybe its been stood a while, any way, didn't seem to clear. I checked the sparks on the one of the left cylinder had no gap whatsoever, so i corrected, only for the problem to reapper soon after start up, checked the plug again, and yep, no gap again, i take it this means the piston or some part of the motor is hitting it, but what exactly? had how do i go about correcting it? looks like i'll start work on the original motor then
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93fxdl
Retro Apprentice
Posts: 58
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Post by 93fxdl on Apr 27, 2011 19:44:35 GMT
first off make sure you have the correct plug and it has a washer on it, next check to see if the head has been helicoiled and the insert hasnt been screwed too far in allowing the plug to contact the piston why not look out for a 400 motor and give yourself some extra beans ttfn glenn
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ikon31
Retro Apprentice
Posts: 51
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Post by ikon31 on Apr 27, 2011 19:53:38 GMT
i wanted to get the bike running coz its my daily (and i've been having to use my '82 2.8 merc, which is killing me!!) i found this motor for cheap and decided on the gamble, pretty disheartining tho
its the correct plug like, i took it out the other motor, i'm pretty sure the washer was on there, but i can be quite stupid coz i've been so busy on it
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Post by TerraRoot on Apr 28, 2011 8:42:16 GMT
try another washer under the spark plug? just to see of that helps, it's probably a big end gone allowing the piston to hit the plug. is there actually bright metal on the spark plug? could it be a you have the wrong plugs entirely?
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ikon31
Retro Apprentice
Posts: 51
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Post by ikon31 on Apr 28, 2011 16:51:30 GMT
i have the recommended plugs, and i have a set of the ones that where in the motor when i got it. Both do the same. Not a bad idea with the washer, i will see if that helps however i fear there are more sinister problems at hand. Well i have two motors now, so i'm sure i can build one good one.... All this glorious weather we are having, and i'm bikeless AGAIN. Think i'll get on ebay
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Post by TerraRoot on Apr 29, 2011 7:50:54 GMT
thats the spirit some, you'll have a back garden like mine in no time(FULL of bikes)!
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ikon31
Retro Apprentice
Posts: 51
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Post by ikon31 on Apr 29, 2011 13:03:15 GMT
i've just moved into a flat, but its got a garage..... let the filling commence!!
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